Currently available information services systems permit a subscriber to the service to obtain information about subscriber-selected topics, such as weather, sports, and stock prices. Several systems enable the subscriber to access the desired information in real-time, via telephone lines. Typically, the subscriber requests information by entering keystrokes from a telephone keypad to transmit a sequence of dual-tone multifrequency (DTMF) telephone signals. The DTMF tones are received at a central processor operated by an information service provider. The information service provider then places one or more telephone calls to various information sources, also via DTMF signaling, to obtain the requested information. The information service provider then transmits the requested information back to the subscriber.
Information retrieval systems which use DTMF signaling to communicate between the information service provider and the information sources suffer several performance disadvantages. In particular, the subscriber must endure long delays while the information service provider obtains the requested information from the information sources. The information retrieval process is slow because specifying information to be retrieved typically may require transmission of twenty five or thirty DTMF tones for each element of information requested. In-band DTMF signaling between the information service provider and the various information sources results in further delays because call setup and other control signals can pass between the information service provider and the information sources only when information is not being delivered to the subscriber.